This invention relates to a pinhole disk laminate for use as an order sorting aperture (OSA) in hard x-ray microscopy using a Fresnel zone plate (FZP). The invention also relates to a process for fabricating the pinhole disk laminate.
According to the invention, the pinhole disk laminate is used as an OSA in highly energetic x-ray microscopy and this enables viewing of very fine structures that have defied observation by conventional x-ray microscopy (roentgenography) on account of its limited spatial resolution.
A potential application of the invention is in the medical field where it is expected to perform satisfactorily enough to take the place of conventional roentgenography. The invention also finds applicability to materials science, where the strong penetrating power of high-energy x-rays which characterizes hard x-ray microscopy is utilized to perform nondestructive inspection and analysis of heavy metals and thick metallic materials as exemplified by nondestructive inspection of nuclear fuel rods, etc.
When applied to biology, high-energy x-rays present so small damage to biosamples that the activities and internal structures of animal and plant can be observed on the site in a viable condition.
The OSA (hereunder referred to as a pinhole disk) is an essential optical element for the development of x-ray microscopes using a Fresnel zone plate (FZP). The existing x-ray microscopes using a FZP have performed satisfactorily well with the conventional thickness of pinhole disks and this is primarily because they use x-rays of low energy. For example, a single metal disk 9.5 mm in diameter have proved satisfactory if it has a round through-hole in the center with a diameter of 20 xcexcm.
However, if the energy of the x-rays used is increased to near 100 keV, even a platinum pinhole disk is insufficient to stop (block) the unwanted hard x-rays diffracted from the FZP in hard x-ray microscopy as long as it has the insufficient thickness.
As shown in FIG. 1, the pinhole disk which is used as a component of a hard x-ray microscope receives hard x-rays coming from the left and the incident light is divided into two parts, one being condensed by a FZP and indicated by 1 in FIG. 1 and the other indicated by 2. The pinhole disk selectively transmits the condensed light 1 of a specified order but blocks the unwanted light 2.
One may think that the above-described problem of failure to stop the unwanted hard x-rays could be solved by increasing the thickness of the pinhole disk. However, making a 20 xcexcm untapered through-hole in a single thick metal disk involves considerable technical limitations and pinhole disks fabricated by the conventional pinhole making technology has been unsuitable for the development of hard x-ray microscopes using the FZP.
The present invention is characterized by bonding or welding a multiple of pinhole disks with the openings of their pinholes kept in alignment. To this end, a wire (e.g. a tungsten wire), a fiber or a pin is passed through the pinholes in the superposed disks which are then bonded (or welded) together with their pinholes kept in alignment. Alternatively, light such as laser light may be guided through the pinholes in the superposed disks which are then secured with their pinholes kept in alignment.
By using the method of the invention, one can fabricate a pinhole disk laminate that has an untapered deep enough hole to stop (block) unwanted hard x-rays. The thickness of the laminate can be adjusted by choosing the number of pinhole disks to be superposed.